Image-forming optical system, illuminating device, and observation apparatus

ABSTRACT

Provided is an image-forming optical system including: image-forming lenses that form a final image and an intermediate image; a wavefront-disturbing element that is placed towards an object from the intermediate image formed by the image-forming lenses and that imparts phase modulation causing a spatial disturbance to the wavefront of light from the object; and a wavefront-restoring element that is placed at a position, between the position and the wavefront-disturbing element being the intermediate image, and that imparts, to the wavefront of the light that has formed the intermediate image, phase modulation canceling out the spatial disturbance imparted by the wavefront-disturbing element, wherein the wavefront-disturbing element and the wavefront-restoring element include optical media and optical media having different refractive indices, and the phase modulation can be imparted by means of the shapes of the interfaces of the optical media and the optical media.

CROSS-REFERENCE TO RELATED APPLICATIONS

This is a continuation of International Application PCT/JP2014/084655 which is hereby incorporated by reference herein in its entirety.

This application is based on Japanese Patent Application No. 2014-207375, the contents of which are incorporated herein by reference.

TECHNICAL FIELD

The present invention relates to an image-forming optical system, an illuminating device, and an observation apparatus.

BACKGROUND ART

There is a known method for moving a focal position in the optical axis direction by adjusting the optical-path length at an intermediate-image position (refer to, for example, Patent Literature 1 below).

CITATION LIST Patent Literature {PTL 1}

Publication of Japanese Patent No. 4011704

SUMMARY OF INVENTION

A first aspect of the present invention is an image-forming optical system including: a plurality of image-forming lenses that form a final image and at least one intermediate image; a first phase modulation element that is placed towards an object from one of the intermediate images formed by the plurality of image-forming lenses and that imparts phase modulation causing a spatial disturbance to a wavefront of light from the object; and a second phase modulation element that is placed at a position, between the position and the first phase modulation element being at least one intermediate image, and that imparts, to the wavefront of the light that has formed the intermediate image, phase modulation for canceling out the spatial disturbance imparted by the first phase modulation element, wherein at least one of the first phase modulation element and the second phase modulation element includes a plurality of optical media having different refractive indices, and the phase modulation can be imparted by means of the shape of an interface of the optical media.

A second aspect of the present invention is an illuminating device including: one of the image-forming optical systems; and a light source that is placed on the object side of the image-forming optical system and that generates illumination light entering the image-forming optical system.

A third aspect of the present invention is an observation apparatus including: one of the image-forming optical systems; and a photodetector that is placed on the final image side of the image-forming optical system and that detects light emitted from an examination object.

A fourth aspect of the present invention is an observation apparatus including: one of the image-forming optical systems; a light source that is placed on the object side of the image-forming optical system and that generates illumination light entering the image-forming optical system; and a photodetector that is placed on the final image side of the image-forming optical system and that detects light emitted from an examination object.

A fifth aspect of the present invention is an observation apparatus including: the above-described illuminating device; and a photodetector that detects light emitted from an examination object illuminated by the illuminating device, wherein the light source is a pulsed laser light source.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a schematic diagram showing an image-forming optical system according to one embodiment of the present invention.

FIG. 2 shows partial magnified views of a wavefront-disturbing element and a wavefront-restoring element in FIG. 1.

FIG. 3 is a diagram for illustrating an intermediate image that is made unclear and a final image that is made clear in the image-forming optical system in FIG. 1.

FIG. 4 is a schematic diagram for illustrating the operation of the image-forming optical system in FIG. 1.

FIG. 5 is a magnified view showing the section from the pupil position on the object side to the wavefront-restoring element in FIG. 4.

FIG. 6 is a schematic diagram showing an image-forming optical system used for a conventional microscope apparatus.

FIG. 7 is a diagram for illustrating a case where the interfaces of the wavefront-disturbing element and the wavefront-restoring element are arranged at optically conjugate positions.

FIG. 8 is a diagram for illustrating, as a reference example of the present invention, a case where the interfaces of the wavefront-disturbing element and the wavefront-restoring element are not arranged at optically conjugate positions.

FIG. 9 is a diagram showing one example of an optical path passing through a depressed part and an optical path passing through a projected part on the interface between two optical media.

FIG. 10 is a diagram showing, as a reference example of the present invention, one example of an optical path passing through a depressed part and an optical path passing through a projected part on the surface of a single optical medium.

FIG. 11 is a schematic diagram showing an image-forming optical system according to one reference embodiment of the invention, serving as a reference example of the present invention.

FIG. 12 is a schematic diagram showing an observation apparatus according to a first embodiment of the present invention.

FIG. 13 is a schematic diagram showing an observation apparatus according to a second embodiment of the present invention.

FIG. 14 is a schematic diagram showing an observation apparatus according to a third embodiment of the present invention.

FIG. 15 is a schematic diagram showing a modification of the observation apparatus in FIG. 14.

FIG. 16 is a schematic diagram showing a first modification of the observation apparatus in FIG. 15.

FIG. 17 is a schematic diagram showing a further modification of the observation apparatus in FIG. 16.

FIG. 18 is a schematic diagram showing a second modification of the observation apparatus in FIG. 15.

FIG. 19 is a schematic diagram showing a third modification of the observation apparatus in FIG. 15.

FIG. 20 shows perspective views of cylindrical lenses, serving as one example of phase modulation elements, used for an image-forming optical system and an observation apparatus according to a reference embodiment of the invention, serving as a reference example of the present invention.

FIG. 21 is a schematic diagram for illustrating an operation in a case where the cylindrical lenses in FIG. 20 are used.

FIG. 22 is a diagram for illustrating the relationship between the amount of phase modulation and optical power based on Gaussian optics, used for the explanation of FIG. 21.

FIG. 23 shows perspective views of binary diffraction gratings, serving as another example of phase modulation elements, used for an image-forming optical system and an observation apparatus according to a reference embodiment of the invention, serving as a reference example of the present invention.

FIG. 24 shows perspective views of one-dimensional sine-wave diffraction gratings, serving as another example of phase modulation elements, used for an image-forming optical system and an observation apparatus according to a reference embodiment of the invention, serving as a reference example of the present invention.

FIG. 25 shows perspective views of free curved surface lenses, serving as another example of phase modulation elements, used for an image-forming optical system and an observation apparatus according to a reference embodiment of the invention, serving as a reference example of the present invention.

FIG. 26 shows longitudinal sectional views of cone lenses, serving as another example of phase modulation elements, used for an image-forming optical system and an observation apparatus according to a reference embodiment of the invention, serving as a reference example of the present invention.

FIG. 27 shows perspective views of concentric binary diffraction gratings, serving as another example of phase modulation elements, used for an image-forming optical system and an observation apparatus according to a reference embodiment of the invention, serving as a reference example of the present invention.

FIG. 28 is a schematic diagram for illustrating the behavior of a ray along the optical axis in a case where diffraction gratings are used as the phase modulation elements.

FIG. 29 is a schematic diagram for illustrating the behavior of the on-axis ray in a case where diffraction gratings are used as the phase modulation elements.

FIG. 30 is a detailed view of the central part for illustrating the operation of the diffraction grating functioning as a wavefront-disturbing element.

FIG. 31 is a detailed view of the central part for illustrating the operation of the diffraction grating functioning as a wavefront-restoring element.

FIG. 32 shows longitudinal sectional views of spherical aberration elements, serving as another example of phase modulation elements, used for an image-forming optical system and an observation apparatus according to a reference embodiment of the invention, serving as a reference example of the present invention.

FIG. 33 shows longitudinal sectional views of irregular shape elements, serving as another example of phase modulation elements, used for an image-forming optical system and an observation apparatus according to a reference embodiment of the invention, serving as a reference example of the present invention.

FIG. 34 is a schematic diagram showing a reflective phase modulation element, serving as another example of the phase modulation element, used for an image-forming optical system and an observation apparatus according to a reference embodiment of the invention, serving as a reference example of the present invention.

FIG. 35 is a schematic diagram showing a gradient index element, serving as another example of a phase modulation element, used for an image-forming optical system and an observation apparatus according to a reference embodiment of the invention, serving as a reference example of the present invention.

FIG. 36 is a diagram showing one example of a lens array in a case where an image-forming optical system of the present invention is applied to an apparatus for microscopically magnified observation for endoscopic use.

FIG. 37 is a diagram showing one example of a lens array in a case where an image-forming optical system of the present invention is applied to a microscope provided with an endoscopic small-diameter objective lens having an inner focus function.

DESCRIPTION OF EMBODIMENTS

An image-forming optical system according to one embodiment of the present invention will now be described with reference to the drawings.

As shown in FIG. 1, an image-forming optical system 1 according to this embodiment includes: one pair of image-forming lenses 2 and 3 placed with a space therebetween; a field lens 4 placed on an intermediate-image forming plane between the image-forming lenses 2 and 3; a wavefront-disturbing element (first phase modulation element) 8 placed in the vicinity of a pupil position PP_(O) of the image-forming lens 2 on an object O side; and a wavefront-restoring element (second phase modulation element) 9 placed in the vicinity of a pupil position PP_(I) of the image-forming lens 3 on an image I side. Reference sign 7 in the figure denotes an aperture stop.

The wavefront-disturbing element 8 and the wavefront-restoring element 9 are arranged at positions optically conjugate to each other, with an intermediate image II formed by the image-forming lens 2 interposed therebetween. Furthermore, the wavefront-disturbing element 8 and the wavefront-restoring element 9 are formed in the shape of, for example, a transparent plate and are composed of a plurality of optical media in the form of a solid or liquid dielectric substance or a transparent conductor.

Solid optical media include optical glass, optical resin, UV-cured resin, crystal material, amorphous material, and so forth. Liquid optical media include water, ethanol, kerosene, corn oil, glycerin, paraffin oil, cedarwood oil, saccharose aqueous solution, a mixture of water and glycerin, a mixture of water and ethanol, liquid crystal, liquid glass, and so forth. If the wavefront-disturbing element 8 and the wavefront-restoring element 9 are to be composed of a solid optical medium and a liquid optical medium, then it is a good idea to hold a stack composed of the solid optical medium and the liquid optical medium between, for example, two parallel flat plates, or alternatively, to hold the liquid optical medium between one parallel flat plate and the solid optical medium.

In this embodiment, the wavefront-disturbing element 8 is composed of a first optical medium 8 a and a third optical medium 8 b having refractive indices different from each other, as shown in FIG. 2. Furthermore, as shown in the same figure, the wavefront-restoring element 9 is composed of a second optical medium 9 a and a fourth optical medium 9 b having refractive indices different from each other.

The first optical medium 8 a of the wavefront-disturbing element 8 and the fourth optical medium 9 b of the wavefront-restoring element 9 have the same refractive index, and the third optical medium 8 b of the wavefront-disturbing element 8 and the second optical medium 9 a of the wavefront-restoring element 9 also have the same refractive index. Thus, the difference from the refractive index of the third optical medium 8 b to the refractive index of the first optical medium 8 a in the wavefront-disturbing element 8 and the difference from the refractive index of the fourth optical medium 9 b to the refractive index of the second optical medium 9 a in the wavefront-restoring element 9 are associated so as to have the same absolute value and opposite signs. Because of this, the wavefront-disturbing element 8 and the wavefront-restoring element 9 have opposite phase characteristics to each other.

Furthermore, the third optical medium 8 b and the second optical medium 9 a have a larger refractive index than the first optical medium 8 a and the fourth optical medium 9 b. Therefore, the wavefront-disturbing element 8 has optical power characteristics equivalent to those of a micro lens array composed of convex lenses, and the wavefront-restoring element 9 has optical power characteristics equivalent to those of a micro lens array of concave lenses.

Furthermore, although the first optical medium 8 a of the wavefront-disturbing element 8 and the second optical medium 9 a of the wavefront-restoring element 9 have refractive indices different from each other, they have the same shape. Thus, the interface between the first optical medium 8 a and the third optical medium 8 b in the wavefront-disturbing element 8 and the interface between the second optical medium 9 a and the fourth optical medium 9 b in the wavefront-restoring element 9 have the same shape. In FIG. 2, reference signs B_(O) and B_(I) denote the interface of the wavefront-disturbing element 8 and the interface of the wavefront-restoring element 9, respectively.

The wavefront-disturbing element 8 and the wavefront-restoring element 9 with this structure can impart, to the wavefront of light, mutually complementary phase modulations by means of the shapes of the interfaces of the optical media. More specifically, when transmitting light that has been emitted from the object O and that has been focused by the image-forming lens 2 on the object O side, the wavefront-disturbing element 8 applies phase modulation that produces a disturbance on the wavefront. As a result of the disturbance being imparted to the wavefront by the wavefront-disturbing element 8, the intermediate image formed by the field lens 4 is made unclear, as shown in FIG. 3. In other words, although an intermediate image focused at one point should, in fact, appear at the position of the field lens 4, the intermediate image II, which has been split into three spots and made unclear, is formed at a position towards the object O from the field lens 4 by the effect of the wavefront-disturbing element 8 equivalent to a micro lens array having positive optical power.

On the other hand, when transmitting light focused by the field lens 4, the wavefront-restoring element 9 imparts, to the wavefront of the light, phase modulation that cancels out the wavefront disturbance imparted by the wavefront-disturbing element 8. As shown in the same figure, the clear final image I is formed by canceling out, with the wavefront-restoring element 9, the wavefront disturbance imparted by the wavefront-disturbing element 8.

Here, the intermediate image II is split into three spots arranged on one plane disposed towards the object O from the field lens 4, and this is because this embodiment is described by way of example of the wavefront-disturbing element 8 including an array of three micro lenses having the same positive optical power such that the array corresponds to the diameter of an incident light beam. However, the intermediate image II can be split into more spots by making each of the micro lenses smaller and thereby manufacturing the wavefront-disturbing element 8 such that more micro lenses correspond to the incident light beam. In addition, the split intermediate image II can be made to disperse in the optical axis direction by producing the micro lenses so as to have not the same optical power but different optical power values. In other words, it is possible to increase the effect of making the intermediate image unclear according to the way of making the micro lenses constituting the wavefront-disturbing element 8. For example, as shown in FIG. 1, the intermediate image II can be split to disperse in the optical axis direction relative to the field lens 4 by mixing micro lenses having positive and negative optical power values, as well as high optical power to low optical power. In addition, if the wavefront-disturbing element 8 is made to have spatially random phase modulation characteristics, instead of a regular shape such as the shape of a micro lens, then the intermediate image II can be made to disperse in a more complicated manner and thus can be made unclear more effectively.

A more general concept of the image-forming optical system 1 according to this embodiment will be described in detail.

In the example shown in FIG. 4, the image-forming optical system 1 is arranged telecentrically with respect to the object O side and the image I side. Furthermore, the wavefront-disturbing element 8 is placed at a position a distance a_(F) away from the field lens 4 towards the object O side, and the wavefront-restoring element 9 is placed at a position a distance b_(F) away from the field lens 4 towards the image I side.

In FIG. 4, reference sign f_(O) denotes the focal length of the image-forming lens 2, reference sign f_(I) denotes the focal length of the image-forming lens 3, reference signs F_(O) and F_(O)′ denote the focal positions of the image-forming lens 2, reference signs F_(I) and F_(I)′ denote the focal positions of the image-forming lens 3, and reference signs II₀, II_(A), and II_(B) denote intermediate images.

Here, the wavefront-disturbing element 8 does not necessarily need to be placed in the vicinity of the pupil position PP_(O) of the image-forming lens 2, and the wavefront-restoring element 9 does not necessarily need to be placed in the vicinity of the pupil position PP_(I) of the image-forming lens 3.

Nonetheless, it is necessary that the wavefront-disturbing element 8 and the wavefront-restoring element 9 be placed at mutually conjugate positions for image formation with the field lens 4, as indicated by Expression (1).

1/f _(F)=1/a _(F)+1/b _(F)  (1)

Here, f_(F) is the focal length of the field lens 4.

FIG. 5 is a diagram showing details of the section from the pupil position PP₀ on the object O side to the wavefront-restoring element 9 in FIG. 4.

In the figure, ΔL is the amount of phase lead, relative to a ray passing through a particular position (i.e., ray height), that is imparted as a result of light passing through the optical elements.

Also, ΔLo(xo) is a function for providing the amount of phase lead of light that passes through an arbitrary ray height x_(O) at the wavefront-disturbing element 8, relative to the light that passes through the optical axis (x=0) at the wavefront-disturbing element 8.

Furthermore, ΔL_(I)(x_(I)) is a function for providing the amount of phase lead of light that passes through an arbitrary ray height x_(I) at the wavefront-restoring element 9, relative to the light that passes through the optical axis (x=0) at the wavefront-restoring element 9.

ΔL_(O)(x_(O)) and ΔL_(I)(x_(I)) satisfy Expression (2) below.

ΔL _(O)(x _(O))+ΔL _(I)(x _(I))=ΔL _(O)(x _(O))+ΔL _(I)(β_(F) ·x _(O))=0  (2)

Here, β_(F) is the lateral magnification due to the field lens 4 in the conjugate relationship between the wavefront-disturbing element 8 and the wavefront-restoring element 9, and is represented by Expression (3) below.

β_(F) =−b _(F) /a _(F)  (3)

When one ray R enters the image-forming optical system 1 as described above and passes through a position x_(O) at the wavefront-disturbing element 8, the ray is subjected to phase modulation of ΔL_(O)(x_(O)) at that position, producing a disturbed ray Rc due to refraction, diffraction, scattering, and so forth. The disturbed ray Rc is projected by the field lens 4 to a position x_(I)=β_(F)·x_(O) on the wavefront-restoring element 9 together with the components of the ray R that have not been subjected to phase modulation. As a result of passing through this position x_(I), the projected ray is subjected to phase modulation of ΔL_(I)(β_(F)·x_(O))=−ΔL_(O)(x_(O)), whereby the phase modulation applied by the wavefront-disturbing element 8 is cancelled out. By doing so, one ray R′ free of wavefront disturbance is restored.

In the case in which the wavefront disturbing element 8 and the wavefront restoring element 9 are in a conjugate positional relationship and also possess the properties according to Expression (2), the ray that has been subjected to phase modulation by passing through a position in the wavefront disturbing element 8 passes through, without exception, a specific position in the wavefront restoring element 9, which is in one-to-one correspondence with the above-described position and at which the phase modulation that cancels out the phase modulation applied by the wavefront disturbing element 8 is applied. With the optical system shown in FIGS. 4 and 5, the above-described effects are exerted on the ray R regardless of the incident position x_(O) and the incident angle thereof in the wavefront disturbing element 8. Specifically, for all types of rays R, it is possible to make the intermediate image II unclear and also to form a sharp final image I.

FIG. 6 shows a conventional image-forming optical system. According to this image-forming optical system, the light focused by the image-forming lens 2 on the object O side forms the clear intermediate image II on the field lens 4 placed on the intermediate-image forming plane and then is focused by the image-forming lens 3 on the image I side, thus forming the clear final image I.

The conventional image-forming optical system has a drawback in that if there is a flaw, dust, or the like on the surface of the field lens 4 or any defect, such as a hollow cavity, in the field lens 4, then the image of the foreign object overlaps the intermediate image clearly formed on the field lens 4, thereby forming the image of the foreign object on the final image I.

In contrast, according to the image-forming optical system 1 of this embodiment, because the intermediate image II that has been made unclear by the wavefront-disturbing element 8 is formed on the intermediate-image forming plane placed at the position corresponding to the field lens 4, the image of the foreign object overlapping the intermediate image II is made unclear due to phase modulation by the wavefront-restoring element 9 when the unclear intermediate image II is made clear by the same phase modulation. Therefore, the image of the foreign object on the intermediate-image forming plane can be prevented from overlapping the clear final image I.

In addition, because each of the wavefront-disturbing element 8 and the wavefront-restoring element 9 is formed of two optical media in which the differences in refractive index have the same absolute value and opposite signs and also both the elements have the same interface shape, the interfaces B_(O) and B_(I) in the wavefront-disturbing element 8 and the wavefront-restoring element 9 can be placed at optically conjugate positions, even from the viewpoint of a three-dimensional shape, as shown in FIG. 7. By doing so, it is possible to make the final image clear by accurately canceling out, with the wavefront-restoring element 9, the disturbance imparted to the light wavefront by the wavefront-disturbing element 8. In FIG. 7, reference sign R_(Ai) and R_(Bi) denote an incident ray (of light), reference signs R_(Ao) and R_(Bo) denote an emitted ray, reference signs B_(OA) and B_(OB) denote intersections of the optical media and the ray in the wavefront-disturbing element 8, and B_(OA)′ and B_(OB)′ denote intersections of the optical media and the ray in the wavefront-restoring element 9. The same also applies to FIG. 8.

Although FIGS. 7 and 8 are depicted as if diffusion light indicated by broken lines occurs at the intersections B_(OA) and B_(OB) and as if convergent light indicated by broken lines is collected at the intersection B_(OA)′ and B_(OB)′, these representations do not necessarily illustrate actual optical phenomena. Rather, these representations are just for the sake of convenience for indicating that the intersection B_(OA) and the intersection B_(OA)′, as well as the intersection B_(OB) and the intersection B_(OB)′, have an optically conjugate positional relationship.

In contrast, as shown in FIG. 8, as a reference example of the present invention, if the refractive indices of optical media 8 a′ and 8 b′ and optical media 9 a′ and 9 b′ of the wavefront-disturbing element 8′ and the wavefront-restoring element 9′ have different differences from each other, the interfaces in the wavefront-disturbing element 8′ and the wavefront-restoring element 9′ cannot be arranged at optically conjugate positions, making it impossible to accurately cancel out, with the wavefront-restoring element 9′, the disturbance imparted to the light wavefront by the wavefront-disturbing element 8′. In FIG. 8, reference sign B_(O′) denotes a conjugate plane to an interface B_(O) in the wavefront-disturbing element 8′.

In addition, because the wavefront-disturbing element 8 and the wavefront-restoring element 9 impart phase modulation to the light wavefront by means of the shapes of the interfaces of a plurality of optical media having different refractive indices, the effect produced by the surface unevenness of those optical media upon the difference in optical-path length is less significant compared with a case where phase modulation is imparted to the light wavefront by means of the surface shape of a single optical medium.

For example, as shown in FIG. 9, assuming that the refractive index of the first optical medium 8 a is n_(A), the refractive index of the third optical medium 8 b is n_(B), and the difference in height of unevenness on the interface between the first optical medium 8 a and the third optical medium 8 b is Δl, the difference ΔP_(b) in optical-path length, as viewed from the optical medium 8 b side, between an optical path I along which the light passes through a depressed part and an optical path II along which the light passes through a projected part at the interface in the optical medium 8 a is represented as ΔP_(b)=Δl(n_(A)−n_(B)). For example, if BK7 is used as the first optical medium 8 a and glycerin is used as the second optical medium 9 a, then ΔP_(b)=0.043Δl, provided that n_(A) of BK7 is 1.516 and n_(B) of glycerin is 1.473.

On the other hand, in a case where a single first optical medium 8 a with a refractive index of n_(A) is disposed in air, as shown in FIG. 10, if the difference in height of unevenness in the first optical medium 8 a is Δl, then the difference ΔP_(a) in optical-path length between the optical path I along which the light passes through a depressed part and the optical path II along which the light passes through a projected part is represented as ΔP_(a)=Δl(n_(A)−1). If, for example, BK7, a type of optical glass, is used as the first optical medium 8 a, ΔP_(a)=0.516Δl, provided that n_(A) of BK7 is 1.516.

Therefore, under the conditions where the magnitude of the unevenness is the same, the effect produced by the interface unevenness in the wavefront-disturbing element 8, composed of the first optical medium 8 a and the third optical medium 8 b, upon the difference in optical-path length is about one tenth of the effect produced by the surface unevenness on a phase modulation element composed of the single first optical medium 8 a upon the difference in optical-path length.

Therefore, according to the image-forming optical system 1 of this embodiment, larger permissible values for dimensional errors are allowed, compared with a case where a phase modulation element composed only of optical media whose surface shapes impart the same accuracy of phase modulation is used, thus facilitating the manufacturing of the image-forming optical system 1. Furthermore, compared with a case where phase modulation is imparted to the light wavefront by means of the surface shapes of optical media having the same dimensional errors, more accurate phase modulation can be imparted.

In this embodiment, the material of the first optical medium 8 a may be the same as that of the fourth optical medium 9 b, and the material of the second optical medium 9 a may be the same as that of the third optical medium 8 b. By doing so, even if there is a problem such as variations in refractive index of optical media depending on, for example, production lot, a change in the environment, or a change over time, a shift in phase modulation resulting from such a problem can be cancelled out between the wavefront-disturbing element 8 and the wavefront-restoring element 9. Therefore, the effect of the wavefront-restoring element 9 to make the image clear becomes more accurate.

Although the two image-forming lenses 2 and 3 have been described as being arranged telecentrically, they are not limited to this arrangement. The same effect can also be achieved with a non-telecentric system.

In addition, although the function for the amount of phase lead has been described as a one-dimensional function, the same effect can also be achieved with a two-dimensional function.

Furthermore, the spaces between the image-forming lens 2, the wavefront-disturbing element 8, and the field lens 4, as well as the spaces between the field lens 4, the wavefront-restoring element 9, and the image-forming lens 3, are not necessarily required. The spaces between these elements may be optically bonded.

Furthermore, although the image forming function and the pupil relaying function have been separately assigned to the lenses constituting the image-forming optical system 1, namely, the image-forming lenses 2 and 3 and the field lens 4, one lens may have both the image forming function and the pupil relaying function simultaneously in the actual image-forming optical system. Also in such a case, the wavefront-disturbing element 8 can impart a disturbance to the wavefront to make the intermediate image II unclear, and the wavefront-restoring element 9 can cancel out the disturbance on the wavefront to make the final image I clear, provided that the above-described conditions are satisfied.

This embodiment can be modified as described below.

In this embodiment, it has been assumed that each of the wavefront-disturbing element 8 and the wavefront-restoring element 9 is composed of a plurality of optical media having different refractive indices. A first modification may be such that only one of the wavefront-disturbing element 8 and the wavefront-restoring element 9 is composed of a plurality of optical media having different refractive indices, thereby allowing phase modulation to be imparted to the light wavefront by means of the shape of the interface between these optical media.

In addition, in this embodiment, it has been assumed that the third optical medium 8 b and the second optical medium 9 a have a larger refractive index than the first optical medium 8 a and the fourth optical medium 9 b. A second modification may be such that the first optical medium 8 a and the fourth optical medium 9 b have a larger refractive index than the third optical medium 8 b and the second optical medium 9 a. By doing so, the wavefront-disturbing element 8 has optical power characteristics equivalent to those of a micro lens array composed of concave lenses, and the wavefront-restoring element 9 has optical power characteristics equivalent to those of a micro lens array composed of convex lenses. Also in this case, the same effect as in this embodiment can be produced.

In this embodiment, it has been assumed that the first optical medium 8 a of the wavefront-disturbing element 8 and the second optical medium 9 a of the wavefront-restoring element 9 have different refractive indices from each other. Instead of this, a third modification may be such that the first optical medium 8 a and the second optical medium 9 a may have the same shape and refractive index.

In this case, it is a good idea for the third optical medium 8 b and the fourth optical medium 9 b to have refractive indices that satisfy a relationship such that the difference from the refractive index of the third optical medium 8 b to the refractive index of the first optical medium 8 a and the difference from the refractive index of the fourth optical medium 9 b to the refractive index of the second optical medium 9 a have the same absolute value and opposite signs.

This ensures that the wavefront-disturbing element 8 and the wavefront-restoring element 9 have the same interface shape and opposite phase characteristics. Therefore, the wavefront-disturbing element 8 and the wavefront-restoring element 9 can be arranged at optically conjugate positions to each other, thereby enhancing the operation of the wavefront-restoring element 9 to make the image clear.

In this modification, the material of the first optical medium 8 a may be the same as that of the second optical medium 9 a. By doing so, it is possible to reduce the cost of phase modulation elements, which have complicated shapes and are difficult to manufacture. Furthermore, in a case where the first optical medium 8 a and the second optical medium 9 a are to be manufactured by molding using, for example, a die, even if an unexpected shape error occurs due to a defect in the die, the error in phase modulation resulting from the shape error in the first optical medium 8 a of the wavefront-disturbing element 8 can be cancelled out by the same shape error in the second optical medium 9 a of the wavefront-restoring element 9 placed at the conjugate position because the first optical medium 8 a and the second optical medium 9 a share the same shape error. Therefore, the operation of the wavefront-restoring element 9 to cancel out the wavefront disturbance (image clarification) can be more enhanced.

In one reference embodiment of the invention, serving as a reference example of the present invention, a wavefront-disturbing element 5 and a wavefront-restoring element 6 each composed of a single optical medium may be employed, as shown in FIG. 11. In this case, it is a good idea for the wavefront-disturbing element 5 and the wavefront-restoring element 6 to have opposite phase characteristics. For example, if the refractive index of the medium constituting the wavefront-disturbing element 5 is equal to the refractive index of the medium constituting the wavefront-restoring element 6, then it is a good idea for the wavefront-disturbing element 5 and the wavefront-restoring element 6 to have mutually complementary surface shapes.

By doing so, it is possible to impart a disturbance to the wavefront by means of the wavefront-disturbing element 5 when it transmits light from the object O, thereby making the intermediate image unclear. On the other hand, it is also possible to cancel out, with the wavefront-restoring element 6 when it transmits the light that has formed the intermediate image, the wavefront disturbance imparted by the wavefront-disturbing element 5.

An observation apparatus 10 according to a first embodiment of the present invention will now be described with reference to the drawings.

As shown in FIG. 12, the observation apparatus 10 according to this embodiment includes a light source 11 for generating non-coherent illumination light; an illumination optical system 12 for irradiating an examination object A with the illumination light from the light source 11; an image-forming optical system 13 for collecting the light from the examination object A; and an image-capturing element (photodetector) 14 for acquiring an image of the light focused by the image-forming optical system 13.

The illumination optical system 12 includes: focusing lenses 15 a and 15 b for focusing the illumination light from the light source 11; and an objective lens 16 for irradiating the examination object A with the illumination light focused by the focusing lenses 15 a and 15 b.

Furthermore, this illumination optical system 12 is so-called Koehler illumination, and the focusing lenses 15 a and 15 b are arranged so that the light emission plane of the light source 11 and the pupil plane of the objective lens 16 are mutually conjugate.

The image-forming optical system 13 is provided with the above-described objective lens (image-forming lens) 16 that is disposed on the object side and that collects observation light (for example, reflected light) emitted from the examination object A; a wavefront disturbing element (first phase modulation element) 17 that disturbs the wavefront of the observation light collected by the objective lens 16; a first beam splitter 18 that splits off the light whose wavefront has been disturbed from the illumination optical path from the light source 11; a first pair of intermediate-image-forming-lenses 19 that are disposed so as to have a space therebetween in the optical-axis direction; a second beam splitter 20 that deflects, by 90°, the light that has passed through individual lenses 19 a and 19 b of the first pair of intermediate-image-forming-lenses 19; a second intermediate-image-forming lens 21 that forms an intermediate image by focusing the light that has been deflected by the second beam splitter 20; an optical-path-length changing means 22 that is disposed at an intermediate-image-forming plane of the second intermediate-image-forming lens 21; a pair of intermediate-image-forming lenses 24 that focuses the light returned by the optical-path-length changing means 22 and transmitted through the intermediate-image-forming lens 21 and the second beam splitter 20 to form an intermediate image; an image-forming lens 25 that focuses the light having passed through lenses 24 a and 24 b in the pair of intermediate-image-forming lenses 24 to form the final image; and a wavefront restoring element (second phase modulation element) 23 disposed between the pair of intermediate-image-forming lenses 24 and the image-forming lens 25.

The image-capturing element 14 is a two-dimensional image sensor, such as a CCD or a CMOS. This image-capturing element 14 includes an image-capturing plane 14 a placed at the image-forming position of the final image due to the image-forming lens 25 and is capable of acquiring a two-dimensional image of the examination object A by acquiring an image of the incident light.

The wavefront-disturbing element 17 is placed in the vicinity of the pupil position of the objective lens 16. The wavefront-disturbing element 17 is composed of a plurality of optical media formed of a light-transmittable, optically transparent material, and, when transmitting light, imparts, to the light wavefront, phase modulation according to the shape of the interface between these optical media. In this embodiment, it imparts the required wavefront disturbance when transmitting the observation light from the examination object A

The wavefront-restoring element 23 is also composed of a plurality of optical media formed of a light-transmittable, optically transparent material, and, when transmitting light, imparts, to the light wavefront, phase modulation according to the shape of the interface between these optical media.

The wavefront-disturbing element 17 and the wavefront-restoring element 23 are made to be capable of imparting mutually complementary phase modulations to the light wavefront by means of the shapes of the interfaces between the optical media, in the same manner as with the above-described wavefront-disturbing element 8 and the wavefront-restoring element 9. Therefore, by transmitting the observation light reflected in a folded manner at the optical-path-length changing means 22, the wavefront-restoring element 23 imparts, to the wavefront of the light, phase modulation that cancels out the wavefront disturbance imparted by the wavefront-disturbing element 17.

The optical-path-length changing means 22, serving as an optical axis (Z-axis) scanning system, includes a plane mirror 22 a placed orthogonally to the optical axis; and an actuator 22 b for displacing the plane mirror 22 a in the optical axis direction. When the plane mirror 22 a is displaced in the optical axis direction through the operation of the actuator 22 b of the optical-path-length changing means 22, the optical-path length between the second intermediate-image forming lens 21 and the plane mirror 22 a is changed, thereby causing a position in the examination object A conjugate to the image-capturing plane 14 a, namely, the focal position in front of the objective lens 16, to be changed in the optical axis direction.

In order to observe the examination object A by the use of the observation apparatus 10 according to this embodiment with this structure, the illumination optical system 12 irradiates the examination object A with the illumination light from the light source 11. The observation light emitted from the examination object A is collected by the objective lens 16, passes through the wavefront-disturbing element 17, passes through the first beam splitter 18 and the pair of intermediate-image forming lenses 19, and is then deflected by 90° at the second beam splitter 20. Then, the observation light passes through the second intermediate-image forming lens 21 and is then reflected in a folded manner at the plane mirror 22 a of the optical-path-length changing means 22, and passes through the wavefront-restoring element 23 via the beam splitter 20 and the pair of intermediate-image forming lenses 24. By doing so, the final image formed by the image-forming lens 25 is acquired by the image-capturing element 14.

When the actuator 22 b of the optical-path-length changing means 22 is operated to move the plane mirror 22 a in the optical axis direction, the optical-path length between the second intermediate-image forming lens 21 and the plane mirror 22 a can be changed. By doing so, the focal position in front of the objective lens 16 can be moved in the optical axis direction for scanning. Then, a plurality of images focused at different positions in the depth direction of the examination object A can be acquired by capturing an image of the observation light at different focal positions. Furthermore, an image with a large depth of field can be acquired by combining the plurality of images through arithmetic averaging and then applying high-band enhancement processing to them.

In this case, an intermediate image is formed by the second intermediate-image forming lens 21 in the vicinity of the plane mirror 22 a of the optical-path-length changing means 22. This intermediate image is made unclear by the effect of the wavefront disturbance imparted by the wavefront-disturbing element 17. Then, after the unclear intermediate image has been formed, the light is focused by the second intermediate-image forming lens 21 and the pair of intermediate-image forming lenses 24 and is then made to pass through the wavefront-restoring element 23, thus causing the wavefront disturbance to be completely cancelled out.

As a result, with the observation apparatus 10 according to this embodiment, there is an advantage in that, even if foreign objects such as blemishes, dust or the like exist on the surface of the plane mirror 22 a, it is possible to prevent images of the foreign objects from being captured in a final image by being superimposed thereon, and that it is also possible to acquire a sharp image of the examination object A.

Similarly, although the intermediate image formed by the first pair of intermediate-image-forming-lenses 19 also undergoes large changes in the optical-axis direction when the focal-point positions on the examination object A are moved in the optical-axis direction, as a result of these changes, even if the intermediate image coincides with the position of the first pair of intermediate-image-forming-lenses 19, or even in the case in which another optical element additionally exits in the area in which the changes occur, because the intermediate image has been made unclear, it is possible to prevent the images of the foreign objects from being captured in the final image by being superimposed thereon. In this embodiment, when the above-described scanning system is incorporated, no noise image is generated in any of the optical elements disposed in the image-forming optical system even if the light moves in the Z-axis direction.

An illuminating device 28 and an observation apparatus 30 according to a second embodiment of the present invention will now be described with reference to the drawings.

In the description of this embodiment, parts in common with the structures of the above-described observation apparatus 10 according to the first embodiment are denoted with the same reference signs, and a description thereof will be omitted.

As shown in FIG. 13, the observation apparatus 30 according to this embodiment includes: an illuminating device 28 including a laser light source 31 and an image-forming optical system 32 that focuses a laser beam from the laser light source 31 onto an examination object A and that focuses the light from the examination object A; an image-capturing element (photodetector) 33 for acquiring an image of the light focused by the image-forming optical system 32; and a Nipkow disk confocal optical system 34 that is placed between the light source 31 and the image-capturing element 33 and the image-forming optical system 32.

The Nipkow disk confocal optical system 34 includes: two disks 34 a and 34 b arranged in parallel with a space therebetween; and an actuator 34 c for simultaneously rotating those disks 34 a and 34 b. Many micro lenses (not shown in the figure) are arranged in the disk 34 a on the laser light source 31 side, and many pinholes (not shown in the figure) are provided at positions corresponding to the micro lenses in the disk 34 b on the object side. Furthermore, a dichroic mirror 34 d for splitting off the light having passed through the pinholes is fixed in a space between the two disks 34 a and 34 b. The light split off by the dichroic mirror 34 d is focused by a focusing lens 35, and a final image is formed on an image-capturing plane 33 a of the image-capturing element 33, thus acquiring an image.

In the image-forming optical system 32, the first beam splitter 18 and the second beam splitter 20 in the first embodiment are realized by a single beam splitter 36, thereby completely integrating the optical path for irradiating the examination object A with the light passing through the pinholes of the Nipkow disk confocal optical system 34 and the optical path of the light that has been generated in the examination object A and that is incident on the pinholes of the Nipkow disk confocal optical system 34.

The operation of the observation apparatus 30 according to this embodiment with this structure will be describe below.

According to the observation apparatus 30 of this embodiment, light that is incident upon the image-forming optical system 32 from the pinholes of the Nipkow disk confocal optical system 34 via an image-forming lens 25, a phase modulation element 23, and a pair of intermediate-image forming lenses 24 passes through the beam splitter 36, is focused by a second intermediate-image forming lens 21, and is reflected in a folded manner at a plane mirror 22 a of an optical-path-length changing means 22. After having passed through the second intermediate-image forming lens 21, the light is deflected by 90° by the beam splitter 36 and is focused onto the examination object A by an objective lens 16 through a first pair of intermediate-image forming lenses 19 and a phase modulation element 17.

In this embodiment, the phase modulation element 23 through which a laser beam first passes functions as a wavefront-disturbing element for imparting a disturbance to the wavefront of the laser beam, and the phase modulation element 17 through which the laser beam subsequently passes functions as a wavefront-restoring element for imparting phase modulation that cancels out the wavefront disturbance imparted by the phase modulation element 23.

Therefore, when the light source image formed in the shape of many point light sources through the Nipkow disk confocal optical system 34 is formed by the second intermediate-image forming lens 21 as an intermediate image on the plane mirror 22 a, it is possible to prevent the inconvenience that the image of a foreign object existing on the intermediate-image forming plane overlaps the final image, and this is because the intermediate image formed by the second intermediate-image forming lens 21 is made unclear through the phase modulation element 23.

Furthermore, because the disturbance imparted to the wavefront through the phase modulation element 23 is canceled out through the phase modulation element 17, it is possible to form a clear image of the many point light sources in the examination object A. Then, high-speed scanning can be performed by rotating the disks 34 a and 34 b through the operation of the actuator 34 c of the Nipkow disk confocal optical system 34 to move the image of those many point light sources formed in the examination object A in the XY directions intersecting the optical axis.

On the other hand, light, for example, fluorescence generated at the image-forming position of the image of the point light sources in the examination object A is collected by the objective lens 16 and passes through the phase modulation element 17 and the first pair of the intermediate-image forming lenses 19. Then, the light is deflected by 90° by the beam splitter 36, is focused by the second intermediate-image forming lens 21, and is reflected in a folded manner by the effect of the plane mirror 22 a. Thereafter, the light is focused once again by the second intermediate-image forming lens 21 and passes through the beam splitter 36. Then, the light is focused by the image-forming lens 25 and is formed at the pinhole positions of the Nipkow disk confocal optical system 34.

The light having passed through the pinholes is split off from the optical path continuing from the laser light source 31 by the dichroic mirror 34 d, is focused by the focusing lens 35, and forms a final image at the image-capturing plane 33 a of the image-capturing element 33. In this case, the phase modulation element 17 through which the fluorescence generated in the shape of many spots in the examination object passes functions as a wavefront-disturbing element in the same manner as in the first embodiment, and the phase modulation element 23 functions as a wavefront-restoring element.

Therefore, fluorescence having a disturbance imparted to the wavefront thereof as a result of passing through the phase modulation element 17 forms an unclear intermediate image on the plane mirror 22 a. Then, the fluorescence the wavefront disturbance of which has been completely cancelled out as a result of passing through the phase modulation element 23 forms an image at the pinholes of the Nipkow disk confocal optical system 34. Then, the light is split off by the dichroic mirror 34 d after having passed through the pinholes, is focused by the focusing lens 35, and forms a clear final image at the image-capturing plane 33 a of the image-capturing element 33.

By doing so, with the observation apparatus 30 according to this embodiment, there is an advantage in that, as an illumination apparatus that radiates laser beams onto the examination object A and also as an observation apparatus with which fluorescence generated at the examination object A is captured, it is possible to acquire a sharp final image while preventing images of foreign objects at an intermediate-image-forming plane from being superimposed on the final image by making the intermediate image unclear. In this embodiment, when the above-described scanning system is incorporated, no noise image is generated even if the light moves in the Z-axis direction in any of the optical elements disposed in the image-forming optical system.

An illuminating device 38 and an observation apparatus 40 according to a third embodiment of the present invention will now be described with reference to the drawings.

In the description of this embodiment, parts in common with the structures of the above-described observation apparatus 30 according to the second embodiment are denoted with the same reference signs, and a description thereof will be omitted.

As shown in FIG. 14, the observation apparatus 40 according to this embodiment is a laser-scanning confocal observation apparatus.

This observation apparatus 40 includes: an illuminating device 38 including a laser light source 41 and an image-forming optical system 42 that focuses a laser beam from the laser light source 41 to an examination object A and that focuses the light from the examination object A; a confocal pinhole 43 transmitting the fluorescence focused by the image-forming optical system 42; and a photodetector 44 for detecting the fluorescence having passed through the confocal pinhole 43.

The image-forming optical system 42 includes, as structures different from those of the observation apparatus 30 according to the second embodiment: a beam expander 45 for magnifying the beam diameter of a laser beam; a dichroic mirror 46 that deflects the laser beam and that transmits fluorescence; a galvanometer mirror 47 placed in the vicinity of a position conjugate to the pupil of an objective lens 16; and a third pair of intermediate-image forming lenses 48. In addition, a phase modulation element 23 for imparting disturbance to the wavefront of the laser beam is placed in the vicinity of the galvanometer mirror 47. Reference sign 49 in the figure denotes a mirror.

The operation of the observation apparatus 40 according to this embodiment with this structure will be described below.

According to the observation apparatus 40 of this embodiment, a laser beam emitted from the laser light source 41 is magnified by the beam expander 45 in terms of the beam diameter, is deflected by the dichroic mirror 46, is scanned two-dimensionally by the galvanometer mirror 47, and is incident upon a beam splitter 36 through the phase modulation element 23 and the third pair of intermediate-image forming lenses 48. The operation after being incident on the beam splitter 36 is the same as that of the observation apparatus 30 according to the second embodiment.

More specifically, because the laser beam forms an intermediate image on a plane mirror 22 a of an optical-path-length changing means 22 after having a disturbance imparted to the wavefront thereof by the phase modulation element 23, the intermediate image is made unclear, thereby preventing the overlapping of the image of a foreign object existing on the intermediate-image forming plane. Furthermore, because the wavefront disturbance is cancelled out by a phase modulation element 17 placed at the pupil position of the objective lens 16, a final image that has been made clear can be formed on the examination object A. In addition, the image formation depth of the final image can be adjusted freely by the optical-path-length changing means 22.

On the other hand, the fluorescence generated at the image-forming position of the final image of the laser beam in the examination object A is collected by the objective lens 16 and passes through the phase modulation element 17. Then, the fluorescence travels along the opposite optical path of the laser beam, is deflected by the beam splitter 36, and is focused to the confocal pinhole 43 by an image-forming lens 24 after having passed through the third pair of intermediate-image forming lenses 48, phase modulation element 23, galvanometer mirror 47, and dichroic mirror 46. Then, only the fluorescence having passed through the confocal pinhole 43 is detected by the photodetector 44.

Also in this case, because the fluorescence collected by the objective lens 16 forms an intermediate image after having the disturbance imparted to the wavefront thereof by the phase modulation element 17, the intermediate image is made unclear, thereby preventing overlapping of the image of a foreign object existing on the intermediate-image forming plane. Then, because the wavefront disturbance is cancelled out through the phase modulation element 23, an image that has been made clear can be formed at the confocal pinhole 43, thereby making it possible to efficiently detect the fluorescence generated at the image-forming position of the final image of the laser beam in the examination object A. As a result, an advantage is afforded in that a bright confocal image with high resolution can be acquired. In this embodiment, mounting the scanning system as described above ensures that no noise images occur even if light shifts in the Z-axis direction on any optical element placed in the image-forming optical system.

Although this embodiment has been described by way of an example of a laser-scanning confocal observation apparatus, it may instead be applied to a laser-scanning multiphoton-excitation observation apparatus, as shown in FIG. 15.

This can be achieved by employing an ultra-short pulsed laser beam source as the laser light source 41, removing the dichroic mirror 46 disposed between the galvanometer mirror 47 and the image-forming lens 24, and employing the dichroic mirror 46 instead of the mirror 49.

In an observation apparatus 50 in FIG. 15, it is possible to make the intermediate image unclear and the final image clear by means of the function of the illuminating device for irradiating the examination object A with an ultra-short pulsed laser beam. As for the fluorescence generated in the examination object A, it is collected by the objective lens 16, is focused by a focusing lens 51 without forming an intermediate image after having passed through the phase modulation element 17 and the dichroic mirror 46, and is detected as is by the photodetector 44.

Furthermore, in each of the above-described embodiments, the focal position in front of the objective lens 16 is changed in the optical axis direction by moving the plane mirror for folding back the optical path with the use of the optical-path-length changing means 22 for changing the optical-path length. Instead of this, a structure for changing the optical-path length by moving, with an actuator 62, one lens 61 a of lenses 61 a and 61 b constituting an intermediate-image forming optical system 61 in the optical axis direction may be employed as the optical-path-length changing means, thus configuring an observation apparatus 60 as shown in FIG. 16. Reference sign 63 in the figure denotes another intermediate-image forming optical system.

In an alternative structure, as shown in FIG. 17, another intermediate-image forming optical system 80 may be placed between two galvanometer mirrors 47 constituting a two-dimensional optical scanner, such that the two galvanometer mirrors 47 are accurately arranged at optically conjugate positions to the phase modulation elements 17 and 23, as well as to an aperture stop 81 placed at the pupil of the objective lens 16.

In addition, a spatial light modulation element (SLM) 64, such as a reflecting-type LCOS, may be employed as the optical-path-length varying means, as shown in FIG. 18. By doing so, it is possible to change the front focal-point position of the objective lens 16 in the optical-axis direction at high speed by changing the phase modulation to be applied to the wavefront at high speed by controlling liquid crystals of the LCOS. In FIG. 18, reference sign 52 denotes a pair of intermediate-image-forming lenses that focuses laser light, whose beam diameter has been increased by the beam expander 45, to form an intermediate image, and reference signs 65 are mirrors. In this case, the phase-modulation element 23 may be disposed between the beam expander 45 and the pair of intermediate-image-forming lenses 52, and the phase-modulation element 17 may be disposed between the beam splitter 36 and the objective lens 16.

Alternatively, instead of the spatial light modulation-element 64 like a reflective LCOS, a spatial light modulation element 66 like a transmissive LCOS may be employed, as shown in FIG. 19. The structure can be made easier than that of the reflective LCOS because the mirror 65 is not necessary.

As a means for moving the focal position in the examination object A in the optical axis direction, various types of well-known variable-power optical elements can be used as active optical elements in addition to those described in each of the above-described embodiments (optical-path-length changing means 22, intermediate-image forming optical system 61 and actuator 62, reflective spatial light modulation-element 64, or transmissive spatial light modulation element 66). First, elements having a mechanically movable part include a shape-variable mirror (DFM: Deformable Mirror) and a shape-variable lens using liquid or gel. Similar elements not having a mechanically movable part include a liquid crystal lens or a potassium tantalate niobate (KTN: KTa1-xNbxO3) crystal lens, which controls the refractive index of the medium by means of the electric field, and a lens in which the cylindrical lens effect in an acousto-optic deflector (AOD/Acousto-Optical Deflector) is applied.

All the above-described embodiments in the form of a microscope according to the present invention have some means for moving the focal position in the examination object A in the optical axis direction. Furthermore, compared with means for the same purpose (for moving either the objective lens 16 or the examination object in the optical axis direction) in conventional microscopes, these means for shifting the focal position in the optical-axis direction can dramatically increase the moving speed because the mass of the object to be driven is small or because a physical phenomenon with quick response is used.

This affords an advantage in that it is possible to detect a higher-speed phenomenon in an examination object (e.g., living biological tissue specimen).

In a case where the spatial light modulation-elements 64 and 66, like a transmissive or reflective LCOS, are to be used in a reference embodiment of the invention serving as a reference example of the present invention, it is possible to make the spatial light modulation-elements 64 and 66 carry out the function of the phase modulation element 23. This affords an advantage in that the phase modulation element 23 serving as a wavefront-disturbing element can be omitted, thereby making the structure even simple.

In the above-described example, the phase modulation element 23 has been omitted in a combination of a spatial light modulation-element and a laser-scanning multiphoton-excitation observation apparatus. In the same manner, in a reference embodiment of the invention serving as a reference example of the present invention, the phase modulation element 23 can also be omitted in a combination of a spatial light modulation-element and a laser-scanning confocal observation apparatus. More specifically, in FIGS. 18 and 19, the beam splitter 36 is replaced with the mirror 49; a branch optical path is formed by employing the dichroic mirror 46 between the beam expander 45 and the spatial light modulation-elements 64 and 66; and the image-forming lens 24, the confocal pinhole 43, and the photodetector 44 are employed, thereby making it possible to cause the spatial light modulation-elements 64 and 66 to carry out the function of the phase modulation element 23. The spatial light modulation-elements 64 and 66 in this case operate as wavefront-disturbing elements that impart a disturbance to the wavefront in response to a laser beam from the laser light source 41, whereas they operate as a wavefront-restoring element for canceling out the wavefront disturbance imparted by the phase modulation element 17 in response to the fluorescence from the examination object A.

For the phase modulation element of the above-described reference embodiment, cylindrical lenses 68 and 69, for example, may be employed, as shown in FIG. 20.

In this case, the cylindrical lens 68 causes the intermediate image in the form of a point image to be elongated in a line shape by the effect of astigmatism, thereby making the intermediate image unclear. Furthermore, the final image can be made clear by the use of the cylindrical lens 69 of the shape complementary to that of the cylindrical lens 68.

In the case of FIG. 20, either a convex lens or a concave lens may be used as a wavefront-disturbing element and as a wavefront-restoring element.

The operation in a case where cylindrical lenses 5 and 6 are used as phase modulation elements will be described in detail below. FIG. 21 illustrates the cylindrical lenses 5 and 6 in a case where they are used as the phase modulation elements in FIGS. 4 and 5. {0094}

In this example, the following conditions are set in particular.

(a) A cylindrical lens having refractive power ψ_(Ox) in the x direction is used as the phase modulation element (wavefront-disturbing element) 5 on the object O side.

(b) A cylindrical lens having refractive power ψ_(Ix) in the x direction is used as the phase modulation element (wavefront-restoring element) 6 on the image I side.

(c) Let the position (height of the ray), in the cylindrical lens 5, of an on-axis ray Rx on the xz plane be x_(O).

(d) Let the position (height of the ray), in the cylindrical lens 6, of an on-axis ray Rx on the xz plane be x_(I).

In FIG. 21, reference signs II_(OX) and II_(OY) denote intermediate images.

Before the operation in this example is described, the relationship between the amount of phase modulation and optical power based on Gaussian optics will be described with reference to FIG. 22.

Assuming that the thickness of the lens at the height (distance from the optical axis) x is d(x) and that the thickness of the lens at the height 0 (on the optical axis) is d₀ in FIG. 22, the optical-path length L(x) from the incident-side tangent plane to the emission-side tangent plane, along the ray at the height x, is represented by Expression (4) below.

L(x)=(d ₀ −d(x))+n·d(x)  (4)

The difference between the optical-path length L(x) at the height x and the optical-path length L(0) at the height 0 (on the optical axis) is represented by Expression (5) below using the thin lens approximation.

L(x)−L(0)=(−x ²/2)(n−1)(1/r ₁−1/r ₂)  (5)

The above-described difference L(x)−L(0) in optical-path length has the same absolute value as and opposite sign of, the amount of phase lead of emitted light at the height x relative to the emitted light at the height 0. Therefore, the above-described amount of phase lead is represented by Expression (6) below, in which the sign in Expression (5) is reversed.

L(0)−L(x)=(x ²/2)(n−1)(1/r ₁−1/r ₂)  (6)

On the other hand, the optical power ψ of this thin lens is represented by Expression (7) below.

ψ=1/f=(n−1)(1/r ₁−1/r ₂)  (7)

Therefore, on the basis of Expressions (6) and (7), the relationship between the amount of phase lead L(0)−L(x) and the optical power ψ is calculated from Expression (8) below.

L(0)−L(x)=ψ−x ²/2  (8)

Now, the description with reference to FIG. 21 will resume.

The amount of phase lead ΔL_(Oc) exerted on the on-axis ray Rx on the xz plane in the cylindrical lens 5, relative to the on-axis chief ray, namely, ray R_(A) along the optical axis is represented by Expression (9) below on the basis of Expression (8).

ΔL _(Oc)(x _(O))=L _(Oc)(0)−L _(Oc)(x _(O))=ψ_(Ox) ·x _(O) ²/2  (9)

Here, L_(Oc)(x_(O)) is a function for the optical-path length from the incident-side tangent plane to the emission-side tangent plane, along the ray of height x_(O) in the cylindrical lens 5.

In the same manner, the amount of phase lead ΔL_(Ic) exerted on the on-axis ray Rx on the xz plane in the cylindrical lens 6, relative to the on-axis chief ray, namely, ray R_(A) along the optical axis, is represented by Expression (10) below.

ΔL _(Ic)(x _(I))=L _(Ic)(0)−L _(Ic)(x _(I))=ψ_(Ix) ·x _(I) ²/2  (10)

Here, L_(Ic)(x_(I)) is a function for the optical-path length from the incident-side tangent plane to the emission-side tangent plane, along the ray of height x_(I) in the cylindrical lens 6.

By applying Expressions (9) and (10), as well as the relationship (x_(I)/x_(O))²=β_(F) ², to Expression (2) shown above, the conditions required for the cylindrical lens 5 to function for wavefront disturbance and for the cylindrical lens 6 to function for wavefront restoration in this example are obtained as shown in Expression (11).

ψ_(Ox)/ψ_(Ix)=−β_(F) ²  (11)

More specifically, the ψ_(Ox) value and the ψ_(Ix) value need to have opposite signs from each other, and the ratio between those absolute values needs to be proportional to the square of the lateral magnification of the field lens 4.

Here, although the description has been given on the basis of the on-axis ray, the cylindrical lenses 5 and 6 also function to disturb and restore the wavefront of an off-axis ray in the same manner, as long as they satisfy the above-described conditions.

Furthermore, in the above-described reference embodiments of the invention serving as reference examples of the present invention, one-dimensional binary diffraction gratings as shown in FIG. 23, one-dimensional sine-wave diffraction gratings as shown in FIG. 24, free curved surface lenses as shown in FIG. 25, cone lenses as shown in FIG. 26, or concentric binary diffraction gratings as shown in FIG. 27 may be employed, instead of a cylindrical lens, for the phase modulation elements 5, 6, 68, and 69 (indicated as the phase modulation elements 5 and 6 in the figure). Concentric diffraction gratings are not limited to the binary type, but any type, including the blazed type and the sine wave type, can be employed.

Diffraction gratings 5 and 6 used as wavefront modulation elements will now be described in detail.

In the intermediate image II in this case, one point image is split into a plurality of point images through diffraction.

Through this operation, the intermediate image II is made unclear, thereby preventing the image of a foreign object on the intermediate-image forming plane from overlapping the final image.

In a case where the diffraction gratings 5 and 6 are used as phase modulation elements, one example of a preferable pathway of the on-axis chief ray, namely, the ray R_(A) along the optical axis is shown in FIG. 28, and one example of a preferable pathway of the on-axis ray R_(X) is shown in FIG. 29. In these figures, each of the rays R_(A) and R_(X) is split into a plurality of diffracted light beams via the diffraction grating 5 and returns to the original one ray via the diffraction grating 6.

Also in this case, the above-described effect can be achieved by satisfying Expressions (1) through (3) above.

Here, in accordance with FIGS. 28 and 29, Expression (2) can be rephrased as “the sum of phase modulation exerted on one on-axis ray R_(X) at the diffraction gratings 5 and 6 is always equal to the sum of phase modulation exerted on the on-axis chief ray R_(A) at the diffraction gratings 5 and 6.”

Furthermore, in a case where the diffraction gratings 5 and 6 have a periodic structure, if their shapes (i.e., phase modulation characteristics) satisfy Expression (2) in an area equivalent to one period, they can also be regarded as satisfying Expression (2) in other areas.

Hence, descriptions will be given with attention focused on the central part, namely, an area in the vicinity of the optical axis of the diffraction gratings 5 and 6. FIGS. 30 and 31 are detailed views of the central parts of the diffraction grating 5 and the diffraction grating 6, respectively.

In this case, conditions required for the diffraction gratings 5 and 6 to satisfy Expression (2) are as follows.

More specifically, the period p_(I) of modulation in the diffraction grating 6 needs to be equal to the period p_(O) of modulation due to the diffraction grating 5 as projected via the field lens 4. In addition, the phase of modulation due to the diffraction grating 6 needs to be reversed to the phase of modulation due to the diffraction grating 5, as projected by the field lens 4, and also, the magnitude of phase modulation due to the diffraction grating 6 needs to be equal to the magnitude of the phase modulation due to the diffraction grating 5 in terms of absolute value.

First, the condition for the period p_(I) and the projected period p_(O) to be equal is represented by Expression (12).

p _(I)=|β_(F) |·p _(O)  (12)

Next, in order that the phase of modulation due to the diffraction grating 6 is reversed to the phase of projected modulation due to the diffraction grating 5, not only does the diffraction grating 5 need to be placed, for example, so that one of the centers in its crest regions coincides with the optical axis, but also the diffraction grating 6 needs to be placed so that one of the centers in its trough regions coincides with the optical axis, in addition to the above-described Expression (12) being satisfied. FIGS. 30 and 31 are just one example of them.

Lastly, conditions for the magnitude of phase modulation due to the diffraction grating 6 and the magnitude of phase modulation due to the diffraction grating 5 to be equal in terms of absolute value are examined.

From optical parameters (crest region thickness t_(Oc), trough region thickness t_(Ot), and refractive index n_(O)) of the diffraction grating 5, the amount of phase lead ΔL_(Odt) exerted on the on-axis ray R_(X) passing through a trough region of the diffraction grating 5, relative to the ray R_(A) (passing through a crest region) along the optical axis, is represented by Expression (13) below.

ΔL _(Odt) −n _(O) ·t _(Oc)−(n _(O) ·t _(Ot)+(t _(Oc) −t _(Ot)))=(n _(O)−1)(t _(Oc) −t _(Ot))  (13)

In the same manner, from optical parameters (crest region thickness t_(Ic), trough region thickness t_(It), and refractive index n_(I)) of the diffraction grating 6, the amount of phase lead ΔL_(Idt) exerted on the on-axis ray R_(X) passing through a crest region of the diffraction grating 6, relative to the ray R_(A) (passing through a trough region) along the optical axis, is represented by Expression (14) below.

ΔL _(Idt)=(n _(I) ·t _(It)+(t _(Ic) −t _(It)))−n _(I) ·t _(Ic)=−(n _(I)−1)(t _(Ic) −t _(It))  (14)

In this case, because the value of ΔL_(Odt) is positive and the value of ΔL_(Idt) is negative, conditions for the absolute values of both the values to be equal are represented by Expression (15) below.

ΔL _(Odt) +ΔL _(Idt)=(n _(O)−1)(t _(Oc) −t _(Ot))−(n ₁−1)(t _(Ic) −t _(It))=0  (15)

Here, although the descriptions have been given on the basis of the on-axis ray, the diffraction grating 5 functions for wavefront disturbance, and the diffraction grating 6 functions for wavefront restoration, as long as they satisfy the above-described conditions.

Furthermore, although the cross-sectional shape of the diffraction gratings 5 and 6 has been assumed to be a pedestal shape in this example, it is needless to say that other shapes can also exhibit the same function.

Furthermore, in the reference embodiments of the invention serving as reference examples of the present invention, spherical aberration elements as shown in FIG. 32, irregular shape elements as shown in FIG. 33, a reflective wavefront modulation element combined with the transmissive spatial light modulation-element 64 as shown in FIG. 34, or gradient index elements as shown in FIG. 35 may be employed as the phase modulation elements 5 and 6.

Furthermore, a fly-eye lens or a micro lens array in which many micro lenses are arranged, or alternatively, a micro prism array in which many micro prisms are arranged may be employed as the phase modulation elements 5 and 6.

In addition, in a case where the image-forming optical system 1 according to the above-described embodiments is to be applied to an endoscope, it is a good idea to place the wavefront-disturbing element 8 in an objective lens (image-forming lens) 70 and to place the wavefront-restoring element 9 in the vicinity of an eyepiece 73 placed on the opposite side of a relay optical system 72, including the plurality of field lenses 4 and a focusing lens 71, from the objective lens 70, as shown in FIG. 36. By doing so, the intermediate image formed in the vicinity of the surfaces of the field lenses 4 can be made unclear, and the final image formed by the eyepiece 73 can be made clear.

In addition, as shown in FIG. 37, the wavefront disturbing element 8 may be provided in an endoscopic small diameter objective lens 74 including an inner focusing function, in which a lens 61 a is driven by an actuator 62, and the wavefront restoring element 9 may be disposed in the vicinity of the pupil position of a tube lens (image-forming lens) 76 provided in a microscope main body 75. As in this configuration, although the actuator itself may be a known lens driving means (for example, a piezoelectric element), it is important that the arrangement allows spatial modulation of the intermediate image from the standpoint of moving the intermediate image on the Z axis, similarly to the above-described embodiments.

In the above-described embodiments, the case where an intermediate image that is made unclear by spatial modulation is applied to the image-forming optical system of an observation apparatus has been discussed, from the standpoint of moving the intermediate image on the Z axis. Similarly, this may also be applied to an observation apparatus, from the standpoint of moving the intermediate image on the XY axis (or XY plane), which is another standpoint.

The above-discussed phase-modulating elements for the image-forming optical system of the present invention may have an aspect described below, and a person skilled in the art could consider the most appropriate embodiment, on the basis of the idea described below. According to the following aspect, because phase-modulating elements for an image-forming optical system characterized by having a configuration for adjusting or increasing spatial disturbance and canceling out of the disturbance applied by the above-described (a pair of) phase-modulating elements, it may be said that it is possible to develop the unique advantageous effect provided by the phase-modulating elements of the present invention or to make it advantageous in practical use.

(1) Periodic Unevenness Structured Phase Modulation Element

For example, in the invention serving as a reference example of the present invention, an image-forming optical system may be characterized in that the first phase-modulation element for making images unclear and the second phase-modulation element for recovery have such a shape that the modulation distribution in a region where the phase is advanced with respect to the average value of the phase-modulation distribution and the modulation distribution in a region where the phase is delayed with respect to the average value are symmetrical with respect to the average value, and in that a plurality of pairs of the phase-advancing region and the phase-delaying region are formed periodically. By using two phase-modulation elements having the same shape and by appropriately arranging them in an optical system in this way, complementary phase modulations can be performed, that is, an intermediate image can be made unclear with the first phase-modulation element and the final image can be made clear with the second phase-modulation element, and hence, the intermediate-image problem can be solved. Herein, there is no need to prepare two different types of phase-modulation element, and only one type is sufficient. Hence, it is possible to manufacture the apparatus easily and to reduce the cost.

Furthermore, in the invention serving as a reference example of the present invention, the first and the second phase-modulation elements may perform phase modulation by means of the surface shape of an optical medium (for example, a shape in which shapes each composed of a recessed portion and a projecting portion are periodically arranged). This makes it possible to produce the necessary phase-modulation elements by the same manufacturing method as typical phase filters. Furthermore, the first and the second phase-modulation elements may perform phase modulation by means of the interface shapes of a plurality of optical media. This enables more precise phase modulation than those having the same optical medium shape accuracy. Alternatively, the phase-modulation elements can be produced with lower optical-medium shape accuracy, in other words, at a lower cost, than those having the same phase modulation accuracy. Furthermore, the first and the second phase-modulation elements may have one-dimensional phase distribution characteristics. By doing so, the intermediate image can be made unclear effectively. Furthermore, the first and the second phase-modulation elements may have two-dimensional phase distribution characteristics. By doing so, the intermediate image can be made unclear effectively.

(2) Liquid-Crystal Phase Modulation Element

Furthermore, in the invention serving as a reference example of the present invention, the above-described first and second phase modulation elements may constitute an image-forming optical system so as to have liquid crystal sandwiched between a plurality of substrates. By doing so, the intermediate image can be made unclear by splitting, into a plurality of focusing points, one focusing point in the intermediate image via the first phase modulation element on the basis of the birefringence of the liquid crystal, and furthermore, the final image can be made clear by restoring the split focusing points into one point via the second phase modulation element, thereby making it possible to solve the problem with the intermediate image. In this case, compared with other birefringent materials, for example, crystal formed of an inorganic material like quartz crystal, the liquid crystal serving as a birefringent material is advantageous in that there are so many types available that design is possible with a high degree of freedom, and also in that the birefringence property is so intense that the intermediate image can be made unclear more effectively.

Furthermore, if the substrate surface in contact with the liquid crystal is a flat surface, the liquid crystal sandwiched between the flat surfaces exhibits the above-described effect of making images unclear as a birefringent prism. In this case, because the surfaces of the substrates sandwiching the liquid crystal are flat surfaces, an advantage is afforded in that processing of the substrates is easier. Furthermore, each of the above-described first and second phase modulation elements may be composed of a plurality of prisms formed of liquid crystal. In this case, each time one prism is added, the number of focusing points in the intermediate image is doubled, causing the intermediate image to be split into more focusing points and thereby increasing the effect of making the intermediate image unclear. In addition, each of the above-described first and second phase modulation elements may have at least one quarter wavelength plate. In this case, as a result of the quarter wavelength plate being used, a high degree of freedom in arranging split focusing points on the intermediate image is ensured. For example, this is preferable in that focusing points split into, for example, four points or eight points can be arranged on a straight line through a plurality of prisms.

In addition, this is preferable in that if the intermediate image points split by the above-described birefringence form an image-forming optical system arranged two-dimensionally, the intermediate image can be made unclear effectively.

In addition, in the invention serving as a reference example of the present invention, the phase modulation elements may be made so that the substrate surface in contact with the liquid crystal has an uneven shape (concave surface, convex surface, concave/convex surface, or non-planar surface). With this structure, the effect of making the intermediate image unclear, intrinsic to an uneven shape (cylindrical surface, toric surface, lenticular surface, micro lens array shape, random surface, and so forth), can be further enhanced through birefringence of the liquid crystal. Alternatively, the above-described first and second phase modulation elements may be designed so that the uneven shapes of the substrates therein are complementary and so that the orientations (directions) of the liquid crystals therein are parallel. According to this design, phase modulation of the two phase modulation elements can be made to have complementary characteristics, namely, allowing the ultimate image (final image) to be restored. Alternatively, the above-described first and second phase modulation elements may be configured so that the uneven shapes of the substrates therein are the same, so that the refractive indices of the glass members constituting the substrates are equal to the mean value of the two principal refractive indices of the above-described liquid crystals, and so that the orientations (directions) of the liquid crystals therein are orthogonal. Also by thing this, phase modulation in the two phase modulation elements can be made to have complementary characteristics; namely, the final image can be restored.

(3) Different Multi-Media Phase Modulation Element

In the present invention, the above-described image-forming optical system may be configured so that the shape of the boundary surface of a plurality of types of optical media functions as phase modulation means. In this case, larger permissible values for dimensional errors are allowed, compared with a normal phase element (the shape of the interface with the air is made to function as phase modulation means). Because of this, not only does manufacturing become easy but also phase modulation can be carried out more accurately with the same dimensional errors. In this case, both the first phase modulation element and the second phase modulation element may be configured so as to come into contact with each other to serve as a plurality of types of optical media having refractive indices different from each other. By making both the phase modulation elements a multi-media type, manufacturing becomes much easier, and phase modulation can be made more accurate.

In addition, the first optical medium section constituting the first phase modulation element and the second optical medium section constituting the second phase modulation element may have the same shape, the second optical medium and the third optical medium that is brought into contact with the first optical medium may have the same refractive index, and the first optical medium and the fourth optical medium that is brought into contact with the second optical medium may have the same refractive index. By doing so, a pair of optical media having a common refractive index can be used for each of the first and second phase modulation elements, so that they have complementary phase modulation characteristics by replacing only the shape relationships. In this case, because the shapes of the interfaces between the optical media in the phase modulation elements are the same, the two phase modulation elements can be arranged in an optically conjugate manner, including the viewpoint of the three-dimensional interface shape, when they are arranged in an optical system, and therefore, the operation of the second phase modulation element to cancel out the wavefront disturbance (make the image clear) becomes more accurate. In addition, by making not only the refractive indices but also the optical media themselves common, even if the refractive indices of optical media have variations for each production lot, for example, or an environmental effect or a change over time occurs, a shift in phase modulation resulting from them is cancelled out between the two phase modulation elements themselves. Thus, the operation of making the image clear can be carried out more accurately by the second phase modulation element.

In addition, the image-forming optical system may be configured such that the first optical medium section constituting the first phase modulation element and the second optical medium section constituting the second phase modulation element have the same shape and the same refractive index and such that Δn₁ and Δn₂ have the same absolute value and opposite signs, where Δn₁ is the difference from the refractive index of the third optical medium that is brought into contact with the first optical medium to the refractive index of the first optical medium and Δn₂ is the difference from the refractive index of the fourth optical medium that is brought into contact with the second optical medium to the refractive index of the second optical medium. For this purpose, it is a good idea that phase elements having the same shape and the same refractive index are used in common for one of a plurality of optical medium sections constituting each of the first and second phase modulation elements. For this common refractive index, it is also a good idea to use a pair of optical media having higher refractive index for one phase modulation element, and to use a pair of optical media having lower refractive index for the other phase modulation element. By making the absolute values of the differences between refractive indices in the pairs equal, it is possible to assign complementary phase modulation characteristics. In this case, because the interface shapes in the phase modulation elements become the same in the same manner as described above, the image is made clear more accurately by the second phase modulation element when the two phase modulation elements are arranged in a conjugate manner. Furthermore, by making common not only the shapes and the refractive indices but also the optical elements themselves in the above-described common section, the cost of the phase modulation elements, which have a completed shape and are difficult to manufacture, can be reduced. Furthermore, in a case where this optical element is to be manufactured by molding using, for example, a die, even if an unexpected shape error occurs due to a defect in the die, the error in phase modulation resulting from the shape error in the first phase modulation element can be cancelled out by the commonly existing shape error in the second phase modulation element placed at the conjugate position because the optical elements share the same shape error. More specifically, the operation of the second phase modulation element to cancel out the wavefront disturbance (make the image clear) is carried out more accurately.

Although the embodiments of the present invention have been described in detail with reference to the drawings, the specific structure is not limited to those of these embodiments but includes design changes etc. that do not depart from the spirit of the present invention. The present invention is not limited to the invention applied to each of the above-described embodiments and their modifications but can be applied to, for example, embodiments in which these embodiments and their modifications are appropriately combined and is not particularly limited.

The above-described embodiments lead to the following invention.

A first aspect of the present invention is an image-forming optical system including: a plurality of image-forming lenses that form a final image and at least one intermediate image; a first phase modulation element that is placed towards an object from one of the intermediate images formed by the plurality of image-forming lenses and that imparts phase modulation causing a spatial disturbance to a wavefront of light from the object; and a second phase modulation element that is placed at a position, between the position and the first phase modulation element being at least one intermediate image, and that imparts, to the wavefront of the light that has formed the intermediate image, phase modulation for canceling out the spatial disturbance imparted by the first phase modulation element, wherein at least one of the first phase modulation element and the second phase modulation element includes a plurality of optical media having different refractive indices, and the phase modulation can be imparted by means of the shape of an interface of the optical media.

According to this aspect, the light entering from the object side is focused by the image-forming lenses, thereby forming the intermediate images and the final image. Here, as a result of the light passing through the first phase modulation element placed towards the object from one of the intermediate images, the spatial disturbance is imparted to the wavefront of the light, causing a blurred intermediate image to be formed. In addition, as a result of the light that has formed the intermediate image passing through the second phase modulation element, the clear final image is formed after the wavefront spatial disturbance imparted by the first phase modulation element has been canceled out.

In other words, as a result of the intermediate images being blurred, even if some optical element is placed in the intermediate-image position and a flaw, foreign object, defect, and so forth are present on the surface of or in the optical element, it is possible to prevent the occurrence of a disadvantage in that the flaw, foreign object, defect, and so forth of the optical element overlap the intermediate images, eventually forming a part of the final image.

In this case, because at least one of the first phase modulation element and the second phase modulation element imparts the phase modulation to the wavefront of light by means of the shape of the interface of the plurality of optical media having different refractive indices, larger permissible dimensional errors can be allowed, compared with optical media that achieve the same accuracy of phase modulation by means of the surface shapes. This can facilitate manufacturing. Furthermore, more accurate phase modulation can be imparted, compared with a case in which phase modulation is imparted to the wavefront of the light by means of the surface shapes of optical media having the same dimensional error.

In the above-described aspect, each of the first phase modulation element and the second phase modulation element may include a plurality of optical media having different refractive indices, and the phase modulation is imparted by means of the shape of an interface of the optical media.

With this structure, manufacturing can be made easier, or phase modulation can be made more accurate.

In the above-described aspect, a first optical medium of the optical media constituting the first phase modulation element and a second optical medium of the optical media constituting the second phase modulation element may have the same shape as each other and different refractive indices from each other, the second optical medium may have the same refractive index as that of a third optical medium of the optical media that forms an interface with the first optical medium, and the first optical medium may have the same refractive index as that of a fourth optical medium of the optical media that forms an interface with the second optical medium.

With this structure, the difference from the refractive index of the third optical medium to the refractive index of the first optical medium and the difference from the refractive index of the fourth optical medium to the refractive index of the second optical medium have a relationship of the same absolute value and opposite signs, thereby allowing the first phase modulation element and the second phase modulation element to have opposite phase characteristics. In this case, as a result of the first optical medium and the second optical medium having the same shape, the first phase modulation element and the second phase modulation element have the same interface shape as each other. Therefore, the first phase modulation element and the second phase modulation element can be arranged in optically conjugate positions, including the viewpoint of the three-dimensional interface shape, and therefore, the operation of the second phase modulation element to cancel out the wavefront disturbance (make the image clear) can be further enhanced.

Note that the first phase modulation element and the second phase modulation element may have the same optical media. By doing so, even if a problem, such as variations in refractive index of optical media depending on, for example, production lot, a change in the environment, or a change over time, occurs, a shift in phase modulation resulting from such a problem can be cancelled out between the first phase modulation element and the second phase modulation element. Therefore, the operation of the second phase modulation element to make the intermediate images clear becomes more accurate.

In the above-described aspect, a first optical medium of the optical media constituting the first phase modulation element and a second optical medium of the optical media constituting the second phase modulation element may have the same shape and refractive index as each other, and the difference from the refractive index of a third optical medium of the optical media that forms an interface with the first optical medium to the refractive index of the first optical medium and the difference from the refractive index of a fourth optical medium of the optical media that forms an interface with the second optical medium to the refractive index of the second optical medium may have a relationship of the same absolute value and opposite signs.

With this structure, the first phase modulation element and the second phase modulation element have the same interface shape and opposite phase characteristics. Therefore, the first phase modulation element and the second phase modulation element can be placed in optically conjugate positions, thereby making image clarification through the second phase modulation element more accurate.

Note that the first phase modulation element and the second phase modulation element may have the same optical media. By doing so, it is possible to reduce the cost of the phase modulation elements, which have complicated shapes and are difficult to manufacture. Furthermore, in a case where these phase modulation elements are to be manufactured by molding using, for example, a die, even if an unexpected shape error occurs due to a defect in the die, the error in phase modulation resulting from the shape error in the first phase modulation element can be cancelled out by the same shape error in the second phase modulation element placed at the conjugate position because the phase modulation elements share the same shape error. Therefore, the operation of the second phase modulation element to cancel out the wavefront disturbance (make the image clear) can be further enhanced.

A second aspect of the present invention is an illuminating device including: one of the image-forming optical systems; and a light source that is placed on the object side of the image-forming optical system and that generates illumination light entering the image-forming optical system.

According to this aspect, when the illumination light emitted from the light source placed on the object side enters the image-forming optical system, the examination object placed on the final image side can be irradiated with the illumination light. In this case, the intermediate images formed by the image-forming optical system are blurred through the first phase modulation element, and therefore, even if some optical element is placed in the intermediate-image position and a flaw, foreign object, defect, and so forth are present on the surface of or in the optical element, it is possible to prevent the occurrence of a disadvantage in that the flaw, foreign object, defect, and so forth of the optical element overlap the intermediate images, eventually forming a part of the final image.

A third aspect of the present invention is an observation apparatus including: one of the image-forming optical systems; and a photodetector that is placed on the final image side of the image-forming optical system and that detects light emitted from an examination object.

According to the image-forming optical system of this aspect, it is possible to detect, with the photodetector, a clear final image that has been formed by preventing the image of a flaw, foreign object, defect, and so forth present on the surface of or in the optical element from overlapping the intermediate images.

A fourth aspect of the present invention is an observation apparatus including: one of the image-forming optical systems; a light source that is placed on the object side of the image-forming optical system and that generates illumination light entering the image-forming optical system; and a photodetector that is placed on the final image side of the image-forming optical system and that detects light emitted from an examination object.

According to this aspect, a clear final image can be acquired over the scanning area of the illumination light in the examination site.

A fifth aspect of the present invention is an observation apparatus including: the above-described illuminating device; and a photodetector that detects light emitted from an examination object illuminated by the illuminating device, wherein the light source is a pulsed laser light source.

According to this aspect, the examination object can be subjected to multiphoton-excitation observation.

One aspect of the invention, serving as a reference example of the present invention, provides a phase modulation element for an image-forming optical system including: a plurality of image-forming lenses for forming a final image and at least one intermediate image; a first phase modulation element that is placed towards an object from one of the intermediate images formed by the image-forming lenses and that imparts spatial disturbance to a wavefront of light from the object; and a second phase modulation element that is placed at a position, between the position and the first phase modulation element being at least one intermediate image, and that cancels out the spatial disturbance imparted by the first phase modulation element to the wavefront of the light from the object, wherein the image-forming optical system has a structure for adjusting or increasing the spatial disturbance and canceling out of the disturbance in the phase modulation elements.

In this description, two aspects of images are used: one representing “clear image” and the other “unclear image” (or “blurred image”).

First, the term “clear image” indicates an image generated through an image-forming lens in a state where no spatial disturbance is imparted to the wavefront of the light emitted from the object or in a state where a disturbance, once imparted, is cancelled out, the “clear image” having a spatial frequency band determined by the light wavelength and the numerical aperture of the image-forming lens, a spatial frequency band similar to it, or a desired spatial frequency band according to the purpose.

Then, the term “unclear image” (or “blurred image”) indicates an image generated through an image-forming lens in a state where spatial disturbance is imparted to the wavefront of the light emitted from the object, the “unclear image” having characteristics for substantially preventing a flaw, foreign object, defect, and so forth present on the surface of or in an optical element placed in the vicinity of the image from being formed as the final image.

An “unclear image” (or an “blurred image”) formed in this way differs from a simple out-of-focus image in that, including an image at a position at which the image was originally supposed to be formed (that is, a position at which the image would be formed if the spatial disturbance were not applied to the wavefront), an unclear image does not have a clear peak of the image contrast over a large area in the optical-axis direction and that the spatial frequency band thereof will always be narrower as compared with the spatial frequency band of a “sharp image”.

The descriptions are based on the above-described concepts of the “sharp image” and the “unclear image” (or the “blurred image”) in this specification, and, in the present invention, moving the intermediate image on the Z axis means to move the intermediate image in a blurred state. Furthermore, Z-axis scanning is not limited solely to the movement of light on the Z axis, but may involve the movement of light on the X and Y, as described below.

With this aspect, the light that has entered the image-forming lenses from the object side is focused by the image-forming lenses, thus forming the final image. In this case, by passing through the first phase modulation element, which is disposed closer to the object than one of the intermediate images, a spatial disturbance is applied to the wavefront of the light, and thus, the intermediate image that is formed is made unclear. In addition, the light that has formed the intermediate image passes through the second phase modulation element, and thus, the spatial disturbance applied to the wavefront thereof by the first phase modulation element is cancelled out. By doing so, in the final-image formation, which is performed after the light passes through the second phase modulation element, it is possible to acquire a clear image. In particular, because of a scanning system, in the light passing through the image-forming optical system, the intermediate image moves on the Z axis while maintaining the above-described spatially modulated state, and thus, during the Z-axis scanning, the intermediate image in a blurred state passes through all the lenses in the image-forming optical system.

Specifically, by making the intermediate image unclear, even if some optical element is disposed at the intermediate image position, and blemishes, foreign objects, defects, or the like exist on the surface of or inside this optical element, it is possible to prevent the occurrence of a problem whereby the blemishes, foreign objects, defects, or the like are superimposed on the intermediate image and are included as part of the finally formed final image. Furthermore, when the present invention is applied to a microscope optical system, even if the intermediate image moving on the Z axis by focusing or the like overlaps a lens located in front of or behind it, a noise image, in which a flaw or foreign matter on the surface of the lens or a defect or the like inside the lens appears in the final image, does not occur.

In the above-described aspect, the first phase modulation element and the second phase modulation element may be placed in the vicinity of the pupil positions of the above-described image-forming lenses.

By doing so, the first phase modulation element and the second phase modulation element can be made compact as a result of being placed in the vicinity of the pupil positions free of variations in light beam.

In addition, in the above-described aspect, an optical-path-length changing means capable of changing the optical-path length between the above-described two image-forming lenses, arranged at positions between which one of the above-described intermediate images is interposed, may be provided.

By doing so, the image-forming position of the final image can be changed easily in the optical axis direction by changing the optical-path length between the two image-forming lenses through the operation of the optical-path-length changing means.

Furthermore, in the above-described aspect, the optical-path-length changing means may be provided with: a plane mirror that is placed orthogonal to the optical axis and that reflects the light for forming the intermediate images so as to be folded back; an actuator for moving the plane mirror in the optical axis direction; and a beam splitter for splitting into two directions the light reflected by the plane mirror.

By doing so, the light from the object side focused by the image-forming lens on the object side is reflected and folded back at the plane mirror, is split off by the beam splitter, and enters the image-forming lens on the image side. In this case, the optical-path length between the two image-forming lenses can easily be changed by operating the actuator to move the plane mirror in the optical axis direction, thereby allowing the image-forming position of the final image to be easily changed in the optical axis direction.

Also in the above-described aspect, a variable spatial phase modulation element for changing the position of the final image in the optical axis direction by changing spatial phase modulation to be imparted to the wavefront of the light may be provided in the vicinity of the pupil position of one of the image-forming lenses.

By doing so, spatial phase modulation that changes the position of the final image in the optical axis direction can be imparted to the wavefront of the light with the variable spatial phase modulation element, and therefore, the image-forming position of the final image can easily be changed in the optical axis direction by adjusting the phase modulation to be imparted.

Furthermore, in the above-described aspect, at least one function of the first phase modulation element and the second phase modulation element may be performed by the variable spatial phase modulation element.

By doing so, the variable spatial phase modulation element can have both the spatial phase modulation that changes the position of the final image in the optical axis direction and the phase modulation for blurring the intermediate image or the phase modulation for canceling out the blurring of the intermediate image. By doing so, the number of component parts can be reduced, thereby making it possible to configure a simple image-forming optical system.

Furthermore, in the above-described aspect, the first phase modulation element and the second phase modulation element may impart, to the wavefront of the light, phase modulation that changes in a one-dimensional direction orthogonal to the optical axis.

By doing so, the intermediate images can be made to blur by using the first phase modulation element to impart, to the wavefront of the light, phase modulation that change in the one-dimensional direction orthogonal to the optical axis, and therefore, even if some optical element is placed in the intermediate-image position and a flaw, foreign object, defect, and so forth are present on the surface of or in the optical element, it is possible to prevent the occurrence of a disadvantage in that the flaw, foreign object, defect, and so forth of the optical element overlap the intermediate images, eventually forming a part of the final image. In addition, a clear final image, free of blurring, can be formed by using the second phase modulation element to impart, to the wavefront of the light, phase modulation for canceling out the phase modulation that has changed in the one-dimensional direction.

Furthermore, in the above-described aspect, the first phase modulation element and the second phase modulation element may impart, to the wavefront of the light beam, phase modulation that changes in a two-dimensional direction orthogonal to the optical axis.

By doing so, the intermediate images can be made to blur more reliably by using the first phase modulation element to impart, to the wavefront of the light, phase modulation that changes in the two-dimensional direction orthogonal to the optical axis. In addition, a clearer final image can be formed by using the second phase modulation element to impart, to the wavefront of the light, phase modulation for canceling out the phase modulation that has changed in the two-dimensional direction.

Furthermore, in the above-described aspect, the first phase modulation element and the second phase modulation element may be a transmissive element that imparts phase modulation to the wavefront when transmitting light.

In addition, in the above-described aspect, the first phase modulation element and the second phase modulation element may be a reflective element that imparts phase modulation to the wavefront when reflecting light.

In addition, in the above-described aspect, the first phase modulation element and the second phase modulation element may have complementary shapes.

By doing so, the first phase modulation element that imparts, to the wavefront, spatial disturbance for blurring the intermediate images and the second phase modulation element that imparts phase modulation for canceling out the spatial disturbance imparted to the wavefront can be easily configured.

Furthermore, in the above-described aspect, the first phase modulation element and the second phase modulation element may impart phase modulation to the wavefront by means of the refractive index profile of a transparent material.

By doing so, wavefront disturbance in accordance with the refractive index profile can be produced when light passes through the first phase modulation element, and phase modulation that cancels out the wavefront disturbance by means of the refractive index profile can be imparted to the wavefront of the light when the light passes through the second phase modulation element.

In addition, another aspect of the invention, serving as a reference example of the present invention, provides an illuminating device including: one of the image-forming optical systems; and a light source that is placed on the object side of the image-forming optical system and that generates illumination light entering the image-forming optical system.

According to this aspect, when the illumination light emitted from the light source placed on the object side enters the image-forming optical system, the illumination object placed on the final image side can be irradiated with the illumination light. In this case, the intermediate images formed by the image-forming optical system are blurred through the first phase modulation element, and therefore, even if some optical element is placed in the intermediate-image position and a flaw, foreign object, defect, and so forth are present on the surface of or in the optical element, it is possible to prevent the occurrence of a disadvantage in that the flaw, foreign object, defect, and so forth of the optical element overlap the intermediate image, eventually forming a part of the final image.

In addition, another aspect of the invention, serving as a reference example of the present invention, provides an observation apparatus including: one of the image-forming optical systems; and a photodetector that is placed on the final image side of the image-forming optical system and that detects the light emitted from the examination object.

According to the image-forming optical system of this aspect, it is possible to detect, with the photodetector, a clear final image that has been formed by preventing the image of a flaw, foreign object, defect, and so forth present on the surface of or in the optical element from overlapping the intermediate images.

In the above-described aspect, the photodetector may be an image-capturing element that is placed at the position of the final image of the image-forming optical system and that acquires the final image.

By doing so, a clear final image can be acquired with the image-capturing element placed at the position of the final image of the image-forming optical system, thereby allowing observation with high accuracy.

In addition, another aspect of the invention, serving as a reference example of the present invention, provides an observation apparatus including: one of the image-forming optical systems; a light source that is placed on the object side of the image-forming optical system and that generates illumination light made to enter the image-forming optical system; and a photodetector that is placed on the final image side of the image-forming optical system and that detects the light emitted from the examination object.

According to this aspect, the light from the light source is focused by the image-forming optical system and radiated on the examination object, and the light generated on the examination object is detected by the photodetector placed on the final image side. By doing so, it is possible to detect, with the photodetector, a clear final image that has been formed by preventing the image of a flaw, foreign object, defect, and so forth present on the surface of or in the intermediate optical element from overlapping the intermediate images.

In the above-described aspect, a Nipkow disk confocal optical system that is placed between the light source and the photodetector and the image-forming optical system may be provided.

By doing so, the examination object can be scanned with multi-point spots of light, thereby allowing a sharp image of the examination object to be acquired at high speed.

Furthermore, in the above-described aspect, the light source may be a laser light source, and the photodetector may be provided with a confocal pinhole and a photoelectric conversion element.

By doing so, the examination object can be observed by means of a clear confocal image without forming the image of a flaw, foreign object, defect, and so forth at the intermediate-image position.

Furthermore, another aspect of the invention, serving as a reference example of the present invention, provides an observation apparatus including: the above-described illuminating device; and a photodetector for detecting the light emitted from the examination object illuminated by the illuminating device, wherein the light source is a pulsed laser light source.

By doing so, the examination object can be observed by means of a clear multiphoton-excitation image without forming the image of a flaw, foreign object, defect, and so forth at the intermediate-image position.

REFERENCE SIGNS LIST

-   I Final image -   II Intermediate image -   O Object -   PP_(O), PP_(I) Pupil position -   1, 13, 32, 42 Image-forming optical system -   2, 3 Image-forming lens -   8 Wavefront-disturbing element (first phase modulation element) -   8 a First optical medium -   9 a Second optical medium -   8 b Third optical medium -   9 b Fourth optical medium -   9 Wavefront-restoring element (second phase modulation element) -   10, 30, 40, 50, 60 Observation apparatus -   11, 31, 41 Light source -   14, 33 Image-capturing element (photodetector) -   17 Phase modulation element (wavefront-disturbing element, first     phase modulation element) -   23 Phase modulation element (wavefront-restoring element, second     phase modulation element) -   20, 36 Beam splitter -   22 Optical-path-length changing means -   22 a Plane mirror -   22 b Actuator -   28, 38 Illuminating device -   34 Nipkow disk confocal optical system -   43 Confocal pinhole -   44 Photodetector (photoelectronic conversion element) -   61 a Lens (optical-path-length changing means) -   62 Actuator (optical-path-length changing means) -   64 Spatial light modulation-element (variable spatial phase     modulation element) 

1. An image-forming optical system comprising: a plurality of image-forming lenses that form a final image and at least one intermediate image; a first phase modulation element that is placed towards an object from one of the intermediate images formed by the plurality of image-forming lenses and that imparts phase modulation causing a spatial disturbance to a wavefront of light from the object; and a second phase modulation element that is placed at a position, between the position and the first phase modulation element being at least one intermediate image, and that imparts, to the wavefront of the light that has formed the intermediate image, phase modulation for canceling out the spatial disturbance imparted by the first phase modulation element, wherein at least one of the first phase modulation element and the second phase modulation element includes a plurality of optical media having different refractive indices, and the phase modulation can be imparted by means of the shape of an interface of the optical media.
 2. The image-forming optical system according to claim 1, wherein each of the first phase modulation element and the second phase modulation element includes a plurality of optical media having different refractive indices, and the phase modulation is imparted by means of the shape of an interface of the optical media.
 3. The image-forming optical system according to claim 2, wherein a first optical medium of the optical media constituting the first phase modulation element and a second optical medium of the optical media constituting the second phase modulation element have the same shape as each other and different refractive indices from each other, the second optical medium has the same refractive index as that of a third optical medium of the optical media that forms an interface with the first optical medium, and the first optical medium has the same refractive index as that of a fourth optical medium of the optical media that forms an interface with the second optical medium.
 4. The image-forming optical system according to claim 2, wherein a first optical medium of the optical media constituting the first phase modulation element and a second optical medium of the optical media constituting the second phase modulation element have the same shape and refractive index as each other, and the difference from the refractive index of a third optical medium of the optical media that forms an interface with the first optical medium to the refractive index of the first optical medium and the difference from the refractive index of a fourth optical medium of the optical media that forms an interface with the second optical medium to the refractive index of the second optical medium have a relationship of the same absolute value and opposite signs.
 5. An illuminating device comprising: the image-forming optical system according to claim 1; and a light source that is placed on the object side of the image-forming optical system and that generates illumination light entering the image-forming optical system.
 6. An observation apparatus comprising: the image-forming optical system according to claim 1; and a photodetector that is placed on the final image side of the image-forming optical system and that detects light emitted from an examination object.
 7. An observation apparatus comprising: the image-forming optical system according to claim 1; a light source that is placed on the object side of the image-forming optical system and that generates illumination light entering the image-forming optical system; and a photodetector that is placed on the final image side of the image-forming optical system and that detects light emitted from an examination object.
 8. An observation apparatus comprising: the illuminating device according to claim 5; and a photodetector that detects light emitted from an examination object illuminated by the illuminating device, wherein the light source is a pulsed laser light source. 